Recent studies have shown that older adults with an estimated glomerular filtration rate (GFR) of less than 60 mL/min/1.73 m2 have a high prevalence of concurrent complications of chronic kidney disease (CKD) and increased risk for adverse outcomes including mortality, cardiovascular disease, and kidney failure.1,2 A prior study demonstrated an increase in CKD prevalence between 1988-1994 and 1999-2004 for the general US population.3

However, trends in CKD prevalence have not been reported for the oldest old (defined as ≥80 years). People aged 80 years or older often have complex medical, social, and psychological needs and substantial requirements for health care resources. This group represents an increasing challenge to the health care system.4

Methods

We used data from the National Health and Nutrition Examination Surveys (NHANES) 1988-1994 and 1999-2010.5 NHANES includes cross-sectional, multistage, stratified probability samples of the US civilian, noninstitutionalized population that can be weighted to produce nationally representative prevalence estimates. We included participants aged 80 years or older who completed a medical evaluation in the NHANES mobile examination center (n = 3558). We excluded participants with missing serum creatinine measurements. Because reduced estimated GFR among older adults is primarily in the mild to moderate range, we excluded those with estimated GFR of less than 15 mL/min/1.73 m2, yielding an analytic sample of 2986 participants. Among those aged 80 years or older, response rates for the NHANES examination were 55.0% to 60.0%.5

NHANES data were collected through interviews and a medical evaluation. Public use NHANES data do not provide exact age for participants aged 80 years or older. Therefore, all participants were assigned an age of 80 years. Estimated GFR was estimated using the Chronic Kidney Disease Epidemiology Collaboration equation. Serum creatinine values were corrected for NHANES 1988-1994, 1999-2000, and 2005-2006.6 The protocol for each NHANES was approved by the US Centers for Disease Control and Prevention institutional review board. Written informed consent was obtained from each participant.

Participant characteristics and the distribution of estimated GFR for US adults aged 80 years or older were calculated for 1988-1994, 1999-2004, and 2005-2010. Linear trends in the prevalence of reduced estimated GFR (45-59 and <45 vs ≥60 mL/min/1.73 m2) over calendar time were evaluated using multinomial logistic regression adjusting for sex, race/ethnicity, hypertension, diabetes, and waist circumference. Calendar time was entered as a continuous variable representing 10-year increments. All analyses were performed using SUDAAN version 10.1 (Research Triangle Institute) with 2-sided statistical tests. P values of less than .05 were considered statistically significant.

Results

The characteristics of participants aged 80 years or older by calendar period appear in Table 1. The prevalence of an estimated GFR of less than 60 mL/min/1.73 m2 was 40.5% (95% CI, 36.4%-44.6%) in 1988-1994, 49.9% (95% CI, 46.2%-53.6%) in 1999-2004, and 51.2% (95% CI, 47.7%-54.7%) in 2005-2010 (P<.001 for each trend). The prevalence of an estimated GFR of less than 45 mL/min/1.73 m2 was 14.3% (11.6%-17.0%) in 1988-1994, 18.6% (15.9%-21.3%) in 1999-2004, and 21.7% (19.0%-24.4%) in 2005-2010 (P<.001 for each trend).

For each 10 years of calendar time (eg, 2010 vs 2000) and compared with an estimated GFR of greater than or equal to 60 mL/min/1.73 m2, the unadjusted odds ratio was 1.22 (95% CI, 1.05-1.42) for an estimated GFR of 45 to 59 mL/min/1.73 m2 and 1.47 (95% CI, 1.20-1.81) for an estimated GFR of less than 45 mL/min/1.73 m2 (Table 2). These trends were partly attenuated but remained statistically significant after adjustment for demographic factors, hypertension, diabetes, and waist circumference.

Discussion

Among US adults aged 80 years or older, the prevalence of an estimated GFR of less than 60 mL/min/1.73 m2 increased from 1988-1994 through 2005-2010. Increases in the prevalence of more severe reductions in estimated GFR (ie, <45 mL/min/1.73 m2) were especially pronounced.

Limitations of the current analysis included lack of data on exact age for NHANES participants and intraindividual longitudinal changes of kidney function and use of a single estimating equation. The increase in reduced estimated GFR may be explained by older US adults with reduced estimated GFR living longer. Along with studies suggesting increased risk for adverse outcomes at lower estimated GFR levels,1,2 the current analysis suggests efforts to address CKD among the oldest old may be necessary.

Conflict of Interest Disclosures: The authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr O’Hare reported receiving royalties from UpToDate; and institutional grants from the US Department of Veterans Affairs, the National Institute on Aging, and the US Centers for Disease Control and Prevention. Dr Muntner reported receiving an institutional grant from Amgen. No other disclosures were reported.

Funding/Support: Support was provided through grant R03AG042336-01 from the National Institute on Aging (Dr Bowling) and the T. Franklin Williams Scholarship Award. Funding was also provided by Atlantic Philanthropies Inc, the John A. Hartford Foundation, the Association of Specialty Professors, the American Society of Nephrology, and the American Geriatrics Society. Additional support was provided by the Birmingham/Atlanta Geriatric Research, Education, and Clinical Center special fellowship in advanced geriatrics and the John A. Hartford Foundation/Southeast Center of Excellence in Geriatric Medicine. The National Health and Nutrition Examination Surveys data were gathered by the National Center for Health Statistics of the US Centers for Disease Control and Prevention with additional support for cardiovascular examination components from the National Heart, Lung, and Blood Institute through interagency agreement Y1-HC-8039.

Role of the Sponsor: The funding sources had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Information: Work on the manuscript was conducted at the Birmingham site of the Birmingham/Atlanta Geriatric Research, Education, and Clinical Center.

Additional Contributions: We thank Richard M. Allman, MD (Birmingham/Atlanta Geriatric Research, Education, and Clinical Center), for his contributions to the manuscript and his continued mentorship. No compensation was provided for his contributions.